改变图片或文字颜色（ Gradient）

using UnityEngine;
using System.Collections;
using System.Collections.Generic;
using UnityEngine.UI;

[AddComponentMenu("UI/Effects/Gradient")]
public class Gradient : BaseVertexEffect {
    [SerializeField]
    private Color32 topColor = Color.white;
    [SerializeField]
    private Color32 bottomColor = Color.black;
    
    public override void ModifyVertices(List<UIVertex> vertexList) {
        if (!IsActive()) {
            return;
        }
        
        int count = vertexList.Count;
        if(count>0){
            float bottomY = vertexList[0].position.y;
            float topY = vertexList[0].position.y;
            
            for (int i = 1; i < count; i++) {
                float y = vertexList[i].position.y;
                if (y > topY) {
                    topY = y;
                }
                else if (y < bottomY) {
                    bottomY = y;
                }
            }
            
            float uiElementHeight = topY - bottomY;
            
            for (int i = 0; i < count; i++) {
                UIVertex uiVertex = vertexList[i];
                uiVertex.color = Color32.Lerp(bottomColor, topColor, (uiVertex.position.y - bottomY) / uiElementHeight);
                vertexList[i] = uiVertex;
            }
        }
    }
}